Thin film arrays used in imagers or liquid crystal displays typically must be coupled to electronic control circuits that are situated off of the wafer on which the array components are disposed. As the number of active components in arrays has increased (e.g., photodetectors in radiation imagers), the electrical connection circuits to enable each component on the array to be addressed have become more complex.
For example, in high resolution large area (e.g., 20 cm.sup.2 or larger) radiation imager arrays comprising about 1,000,000 pixels, about 2000 electrical connections must be made to the components on the substrate. In such arrays, the pitch (center to center spacing) of the contact pads is small, that is, less than about 100 .mu.m. In conventional, low resolution arrays, the pitch of the electrical connection contact pads is greater than about 150 .mu.m.
Conventional methods of making contacts to low resolution arrays include the use of an elastomeric connector material having small (e.g., diameters in the range of 25 .mu.m to 50 .mu.m) conducting particles mixed therein to make electrical contact between the electrically conductive lines on the substrate and the connection lines on a circuit board containing the control circuits; a mechanical clamping device maintains contact between the electrical lines on the array wafer and external circuit connection lines. A second method uses an anisotropic conducting film (ACF) material that comprises an electrically insulating thermoplastic or thermosetting adhesive that has conducting metal particles mixed into the adhesive. The external circuit usually is a flexible printed circuit or a tape automated bonded (TAB) circuit. The ACF material is used to bond the external circuit to the array wafer (e.g., to the portion of the glass substrate with the contact pads) under heat and pressure; contact is made between the external circuit contacts, the metal particles imbedded in the adhesive, and the relatively large area (e.g., corresponding to a pitch greater than about 150 .mu.m) contact pads on the array wafer. Both of these methods are limited to low resolution devices by the density of conducting particles that can be placed in the elastomer or ACF before shorting between adjacent contacts becomes probable. The resolution of standard printed circuit and TAB technology is typically greater than 150 .mu.m and thus also limits the resolution of these schemes.
It is particularly desirable to be able to make electrical contacts between fine pitch imagers (e.g., having a pitch in the range of 10-100 .mu.m) and external control electronics in order to make use of amorphous silicon (a-Si) technology in forming the array thin film circuits; the a-Si technology provides ease of fabrication and consistent uniformity necessary for high yields that is not available from single crystal silicon technology, which has been investigated to provide an alternative means to develop high resolution arrays with small pitch connection requirements.
It is thus an object of this invention to provide a method of coupling a high density thin film circuit (e.g., having contact pads with a pitch less than about 100 .mu.m) to corresponding contacts on an external connector.
It is a further object of this invention to provide an amorphous silicon high density thin film circuit having contact pads of with a pitch in the range of about 10 .mu.m to 100 .mu.m that is coupled to an external control circuit.